pub const MAX_EXPRESSION_DEPTH: usize = 64;Expand description
Maximum permitted AST nesting depth.
Applied during structural validation (parse phase) and during evaluation
to prevent stack exhaustion on pathological inputs such as
((((...1...)))) or long left-associative binop chains like
1+1+...+1 that produce a deep AST even when the source is short.
A limit of 64 is well above any legitimate template expression: the
spec already caps list nesting at 2 and list comprehensions at a
single generator, and real-world expressions rarely exceed ~10
levels of nesting. Exceeding this limit raises
ExpressionErrorKind::ExpressionTooDeep.
See specs/expr/parser.md (Depth limit) and specs/expr/evaluator.md
(Depth limit) for the rationale.